JPH04222284A - Method for recycling and pulping waste heat-sensitive recording paper - Google Patents

Abstract

PURPOSE:To provide a method for obtaining recycled pulp, having high whiteness and excellent in quality by efficiently separating a heat-sensitive recording material from waste heat-sensitive recording paper. CONSTITUTION:In a method for recycling and pulping waste heat-sensitive paper and obtaining recycled pulp from therefrom, the NaOH concentration based on the waste paper is 1.0-10wt.% and a defoaming agent is added into an aqueous solution of NaOH. The aqueous solution of the NaOH is kept at 30-60 deg.C temperature. In this state, waste paper pulp concentration is regulated to >=10wt.% to carry out alkali disintegration of the waste paper. A deinking agent and a peroxide are added to the resultant disintegrated waste paper pulp and the obtained pulp is subjected to mechanical stirring treatment at a high concentration.

Description

Detailed Description of the Invention [0001] [Industrial Application Field] The present invention relates to a method for obtaining recycled pulp using heat-sensitive recording paper waste paper (including waste paper), and particularly relates to a method for obtaining recycled pulp from heat-sensitive recording paper from pulp fibers. This invention relates to a method for pulping waste heat-sensitive recording paper to obtain recycled pulp with good separation and high whiteness. [0002] Generally, a thermosensitive recording material layer comprising a basic colorless dye in the form of fine particles, a coloring agent, a sensitizer, a pigment, a binder, an auxiliary agent, etc. is provided on a base paper made of pulp fibers. Recording paper is widely known. When heat is applied to this thermosensitive recording paper, the sensitizer and coloring agent in that area melt and come into contact with the basic colorless dye, producing a colored image. Colored images produced by thermosensitive recording paper are generally inferior in water resistance, oil resistance, plasticizer resistance, and the like. For this reason, for example, if a colored image comes into contact with water, oil, or a plasticizer contained in a plastic film, the image density will drop significantly, and if the heat-sensitive recording layer is touched by hand during handling, fingerprint-like fogging will occur. It has the following drawbacks. In order to solve the above-mentioned problems, for example, a protective layer such as a water-based emulsion coating layer, a water-soluble polymer compound coating layer, a water-soluble polymer layer cured with a curing agent, etc. is applied on the heat-sensitive recording layer or on the back side. Thermal recording paper provided with this method has come to be widely used in fields such as labels. On the other hand, as the production and demand for thermal recording paper has increased in recent years, the treatment of waste thermal recording paper derived from it has been attracting more attention from an environmental perspective. This is becoming a new issue. [0004] Conventionally, recycled pulp from used newspapers and printed coated paper has been carried out, and generally involves a disintegration process in which waste paper is disintegrated to obtain a pulp suspension, and foreign substances in the pulp suspension are separated. Recycled pulp is produced through a rough selection process, a fine selection process, a deinking process to separate the printing ink, and a bleaching process to whiten the color. [0005] For example, Japanese Patent Publication No. 50-29042 proposes a method for recycling used paper, which consists of disintegration and rough selection of printed coated paper, dehydration, bleaching, and ink separation. No. 6802 discloses a method of disintegration treatment using an alkaline solution containing a surfactant. Furthermore, JP-A-63-135585 discloses a process of disintegrating heat-sensitive recording paper in an alkaline aqueous solution containing a surfactant and then neutralizing the disintegrated waste paper slurry.
A method has been proposed in which recycled materials are recycled through a process of flotation sorting, concentrating with a dehydration squeezer, and disintegrating with a high-speed disintegrator. However, when these methods are applied to waste thermal recording paper, including thermal recording paper that has a protective layer with water resistance, oil resistance, plasticizer resistance, etc., undisintegrated pieces of the protective layer remain, making it difficult to use this pulp. When paper is made, the heat-sensitive recording material develops color during the drying process of the paper machine, reducing the whiteness of the resulting paper. Furthermore, JP-A-2-133688 proposes a method in which a kneading treatment is performed after removing a coloring agent and reducing the weight of the coloring agent remaining in the fibers to be less than the weight of the remaining basic dye. ing. However, even when this method is applied to waste heat-sensitive recording paper that has a protective layer, the protective layer is not sufficiently disintegrated before the next kneading process is carried out, so the basic dye develops color in the kneading process. As a result, pulp with high whiteness cannot be obtained. Due to the above-mentioned circumstances, the conversion of waste heat-sensitive recording paper into recycled pulp is avoided, and the paper is currently treated as industrial waste. [0006] The present invention relates to a method for obtaining recycled pulp using waste heat-sensitive recording paper (including waste paper), and particularly relates to a method for obtaining recycled pulp using a heat-sensitive recording material layer including a protective layer. The purpose of the present invention is to provide a pulping method for obtaining recycled pulp that does not develop color due to heat and has a high degree of whiteness by efficiently separating it from pulp fibers. Means for Solving the Problems [0007] The present invention disintegrates waste heat-sensitive recording paper in an aqueous NaOH solution to form a disintegrated pulp, adds a deinking agent and a peroxide, and then disintegrates the disintegrated pulp. In the method of high-concentration mechanical stirring treatment, the following conditions (a
) to (d) This is a method for converting waste heat-sensitive recording paper into recycled pulp, which is characterized by processing it so as to satisfy the following. (a); The NaOH aqueous solution contains an antifoaming agent (b);
The concentration of NaOH is 1 to 10% by weight based on the waste paper pulp (c); The temperature of the NaOH aqueous solution during disintegration is 30 to 6% by weight
0°C (d); The concentration of waste paper pulp at the time of disintegration is 10% by weight or more. [Action] The waste heat-sensitive recording paper targeted by the present invention includes:
For example, for commercial use such as fax machines, printers, labels, etc.
This includes thermal recording paper used for a wide range of purposes such as office and household use, as well as semi-finished products and waste paper generated in the process of manufacturing such thermal recording paper. As described above, in the waste paper processing method of the present invention, waste heat-sensitive recording paper is first disintegrated with an NaOH aqueous solution under specific conditions using a disintegrator such as a pulper to form a pulp suspension. In this case, the reason why the NaOH solution is used is to promote disintegration of the heat-sensitive recording material layer and to make the coloring agent in the heat-sensitive recording material layer water-soluble. [0010] As a coloring agent, organic acids such as phenolic compounds and aromatic carboxylic acids are generally used, but these become Na salts in Na0H solution and become solubilized in water, making them heat-sensitive. It is eluted from the recording material layer. On the other hand, basic dyes such as triallylmethane-based, phenylmethane-based, thiazine-based, and fluoran-based dyes do not react with the coloring agent in the form of Na salt to develop color. [0011] Here, in order to smoothly perform the action of NaOH with the waste heat-sensitive recording paper, NaOH is added in an amount of 1.0 to 10% by weight, preferably 1.0 to 5% by weight, based on the waste paper.
It is necessary to add within this range. Incidentally, if the amount of NaOH added exceeds 10% by weight, alkaline hydrolysis will occur.
The strength of the resulting recycled pulp decreases. On the other hand, 1.0
If the amount is less than % by weight, the coloring agent in the heat-sensitive recording material layer will not be sufficiently converted to Na salt. In addition, Na0 during disaggregation
When the temperature of the H aqueous solution exceeds 60°C, heat is applied to the heat-sensitive recording material layer before the coloring agent in the heat-sensitive recording material layer turns into Na salt, which develops color and adsorbs to the pulp fibers, resulting in the formation of recycled pulp. This is not preferred because the whiteness decreases. On the other hand, if the temperature is lower than 30°C, the binder contained in the heat-sensitive recording material layer and the resin in the protective layer become hard, and although the base paper layer is disintegrated, the disintegration of the heat-sensitive recording material layer and the protective layer becomes insufficient. . As a result, the coloring agent from the heat-sensitive recording material layer is not sufficiently converted into Na salt before proceeding to the next kneading step, so that the basic dye develops color in the kneading step. Moreover, the disintegration time is also long, which is an economical problem. Therefore, in the present invention, the liquid temperature of the alkaline aqueous solution during disintegration is specified to be 30 to 60°C. In the present invention, in order to efficiently disintegrate waste heat-sensitive recording paper with an alkaline aqueous solution, it is necessary to make the pulp concentration 10% by weight or more. That is, by specifying the pulp concentration to 10% by weight or more, the NaOH concentration in the solution inevitably increases, which not only promotes the disintegration of the base paper but also improves the mechanical bond between the pulp fibers and the heat-sensitive recording material layer. The friction also promotes disintegration of the heat-sensitive recording material layer. Incidentally, if it is 10% by weight or less, the NaOH concentration in the solution will also be low, and disintegration will be that much worse. As a result, in the post-disintegration process, a screen treatment is performed to remove foreign substances contained in the waste paper pulp, but at this time, undisintegrated pulp fibers are removed, reducing the yield of the resulting recycled pulp. It should be noted that if the pulp concentration exceeds 40% by weight, stirring and mixing will become difficult and disintegration will not be possible. Therefore, the pulp concentration at the time of disintegration is specified to be 10 to 40% by weight. [0013] Generally, in order to improve the recording sensitivity of heat-sensitive recording paints, it is necessary to micronize the material in each dispersion to a size of several microns or less during the paint preparation stage of the heat-sensitive recording material. In order to smoothly form particles into fine particles, auxiliary agents such as surfactants and protective colloids are often used during dispersion or wet grinding. Furthermore, since binders such as PVA and latex are used, a large amount of air is trapped in the disintegration (stirring) process of waste heat-sensitive recording paper containing these, resulting in the presence of large amounts of bubbles in the resulting suspension. become. These bubbles significantly reduce cleaning efficiency in processes such as dehydration concentration and washing, and cause heat-sensitive recording material to remain on the surface of the pulp fibers. In addition, the wastewater after dehydration and concentration is subjected to wastewater treatment such as coagulation flotation and coagulation sedimentation and is used as recovered water, but bubbles are generated during the treatment process, causing carryover and reducing wastewater treatment efficiency. Cause. In the present invention, in order to suppress these bubbles, an antifoaming agent is added in the defibration step. By adding an antifoaming agent, the heat-sensitive recording material layer can be efficiently separated from the pulp fibers, and recycled pulp with high whiteness and stable quality can be efficiently obtained. [0014] Specific antifoaming agents include polyglycol/fatty acid mixtures, phosphoric acid esters, silicone emulsion systems, nonionic fatty acid mixtures, polyglycol esters, alcohol systems, vegetable oil systems, fatty acid esters,
Examples include pine oil emulsion, sulfuric ester type, metal soap type, etc. The type thereof is not particularly limited, and may be appropriately selected depending on the type of used paper, liquid temperature, etc. The antifoaming agent may be added generally in an amount of about 0.0001 to 0.1% by weight based on the waste paper. Furthermore, if it is not sufficient to add the antifoaming agent in the disintegrating step, it is of course possible to add it immediately before entering the washing step or dehydration/concentration. In the present invention, the disintegrating machine used is not particularly limited, but a preferred disintegrating machine is preferably a high-density pulper having a helical rotor. When disintegrating waste heat-sensitive recording paper, if the waste paper contains pressure-sensitive adhesives, plastics, etc. (hereinafter simply referred to as foreign substances), it is natural that foreign substances will be mixed into the suspension after disintegration. Therefore, it is necessary to separate these foreign substances. A screening process is provided for the separation. In addition, when disintegrating this waste paper, if these foreign substances are subjected to excessive mechanical action by an agitator or the like, they may be broken into small pieces and slip out through the holes in the screen during the screening process, which may impair the separation effect. Not only that, but the recycled pulp also contains foreign matter. As a result, foreign matter may block the wire openings or contaminate press rolls or blankets during the papermaking process, causing paper breakage and significantly reducing productivity. In addition, it may cause spots on the paper surface, which may adversely affect the quality of the paper. [0016] Therefore, it is important to consider the degree of disintegration so that the foreign matter does not become finer than the holes in the screen. Usually, the screen step is installed at one or more locations after the disintegration step, after the mechanical stirring step, and after the foam flotation separation step. The installation location of the screen is not particularly limited, and may be appropriately selected depending on the amount, type, etc. of foreign matter. The suspension of waste heat-sensitive recording paper thus obtained is dehydrated and concentrated to a pulp concentration of 20% by weight or more. During this dehydration and concentration process, most of the heat-sensitive recording material, such as coloring agents and pigments, which have become Na salts and become water-soluble, are separated and removed from the pulp fibers. Although a known dehydrating and concentrating machine can be used in the dehydrating and concentrating step, a combination of an inclined screw thickener and a screw press is particularly preferably used in order to obtain the desired effects of the present invention. Next, it is necessary to disperse the granular heat-sensitive recording layer into fine particles by mechanically stirring strongly the waste paper pulp suspension whose pulp concentration has been adjusted to 20% by weight or more. Waste heat-sensitive recording paper with a protective layer that has properties such as water resistance, oil resistance, and plasticizer resistance is easily disintegrated in a normal disintegrator, but the heat-sensitive recording layer remains as granular particles. , mixed in the suspension. The thermosensitive recording material is present in these granules and cannot be easily removed. For this purpose, by adjusting the pulp concentration of the suspension to 20% by weight or more and performing mechanical stirring, it becomes possible to disperse the granular particles into fine particles. Incidentally, when the pulp concentration is less than 20% by weight, the dispersion efficiency is poor and granular particles remain in the suspension. A heat-sensitive recording material is contained in the granular particles. In addition, these granular particles cannot be removed by foam flotation separation in the subsequent process. If the pulp concentration exceeds 40% by weight, mechanical stirring and mixing becomes difficult, so the pulp concentration of the pulp suspension when performing mechanical stirring must be adjusted within the range of 20 to 40% by weight. . The method of mechanical stirring in the present invention refers to strong mechanical stirring accompanied by a compressive action, and for example, commonly used stirrers such as kneaders, twin-shaft mixers, and dispersers may be used as appropriate. There are no particular limitations. In addition, in the case of this mechanical stirring treatment, as in the disaggregation process, the heat-sensitive recording material still remains, so in order to suppress the color development of this heat-sensitive recording material, the temperature during the treatment was set to 60°C. It is preferable to maintain the following. After the mechanical high concentration stirring treatment, the pulp concentration is diluted to 2 to 5% by weight and further mechanical stirring is performed. This is because strong mechanical stirring is performed at a pulp concentration of 20% by weight or more in the previous step, so that the pulp fibers become entangled with each other and become ball-like. A portion of the heat-sensitive recording material is incorporated into the tangled hair bulb. This hair-ball-shaped pulp cannot be disentangled using the agitator installed in normal chests. Even if the next step of foam flotation separation is carried out in the state of this bulbous pulp suspension, the heat-sensitive recording material cannot be completely removed, and the whiteness of the obtained recycled pulp is reduced. For this purpose, mechanical stirring is carried out at a pulp concentration of 2 to 5% by weight to disentangle the pulp fibers and form them into single fibers. Equipment used for mechanical stirring at this time includes commonly used high-speed disintegrators, refiners, etc., and is not particularly limited. Furthermore, after adding a deinking agent to the waste paper pulp suspension that has undergone mechanical stirring treatment at a low concentration as described above,
The pulp concentration is adjusted to 0.3 to 1.5% by weight, air is blown into the pulp, and foam flotation separation is carried out to remove the heat-sensitive recording material still remaining in the pulp suspension together with the foam. The deinking agent used at this time can be a commonly used deinking agent for old newspapers, and in particular, a deinking agent consisting of fatty acid soap, fatty acid, and fat-based ethylene oxide/propylene oxide adducts can be used. is a preferred deinking agent because it has a strong tendency to adhere the heat-sensitive recording material to the surface of the bubbles and exhibits excellent effects in flotation and separation of the heat-sensitive recording material together with the bubbles in the bubble flotation process. The amount of deinking agent added is
It may be adjusted as appropriate depending on the foaming condition, and is usually added in an amount of 0.01 to 1.0% by weight based on the dry pulp. The deinking agent may be added at the time of foam flotation separation, but it is preferably added before the mechanical stirring step, especially in the mechanical stirring step when the pulp concentration is 20% by weight or more, so that the deinking agent is suspended in the pulp. This is a desirable embodiment because it is efficiently dispersed in the liquid. Furthermore, if the deinking agent is left to stand for one hour or more after mechanical stirring, the adsorption of the deinking agent to the heat-sensitive recording material becomes better, and the effect of separating the heat-sensitive recording material from the pulp is further improved. The foam flotation device used in the present invention is not particularly limited, and conventional floatators and the like can be used as appropriate. In addition, in the present invention, in order to further increase the whiteness of the recycled pulp obtained in this way, peroxide is added to the pulp suspension before entering the high concentration mechanical stirring step to The trace amount of heat-sensitive recording material remaining is oxidized and bleached. Examples of the peroxide include hydrogen peroxide, sodium peroxide, and sodium percarbonate, and are not particularly limited. The amount of peroxide added should be 0.2 to 5% by weight based on the pulp, and while measuring the whiteness of the pulp,
You can choose as appropriate. In addition, as a stabilizer for peroxide,
One or more selected from the group consisting of sodium silicate, chelating agents, sodium hydroxide, magnesium sulfate, etc., which are used in ordinary peroxide bleaching, are added in combination. [0023] If there are heavy foreign substances in the pulp, it is desirable to perform a cleaner treatment. On the other hand, if there are lightweight foreign substances, it is advisable to provide a lightweight foreign substance separation process such as Giroclean. Furthermore, it is preferable to provide a cleaning step to remove residual bleaching agent, decomposed products of the heat-sensitive recording material, residual deinking agent, and the like. As the cleaning method, displacement cleaning, dilution dehydration cleaning, press cleaning, etc. are used as appropriate. [0024] Furthermore, in order to increase the strength of the paper, it is possible to increase the pulp concentration to 3 to 4% by weight and beat the paper.
The degree of beating may be determined as appropriate depending on the quality target of the paper. The thus obtained white recycled pulp does not develop color during the papermaking process and has extremely few pinholes or speckled minute foreign matter, so it can be effectively used as a raw material for papermaking. [Examples] The present invention will be explained in more detail with reference to Examples below, but the present invention is of course not limited to these. In addition, % in an example shows "weight%." Example 1 [Disintegration process] Waste heat-sensitive recording paper having a protective layer on a pulper (manufactured by Aikawa Iron Works; high-concentration pulper), 1.5% NaOH was added to the waste paper, and an antifoaming agent ( Nopco 1407-K/manufactured by San Nopco Co., Ltd.) was added at 0.01% based on the dry solid content, and the pulp concentration was 1.
Warm water (55°C) was added so that the concentration was 5%, and the mixture was disintegrated for 30 minutes. [Screening process] The pulp suspension obtained above was diluted to a pulp concentration of 3.5%, and was screened using a screen with a slit width of 0.2 mm (Fine Screen/manufactured by Aikawa Iron Works). Processed. [Mechanical stirring step] Next, the accept was dehydrated and concentrated using a dehydration concentrator (tilt extractor, screw press, manufactured by Aikawa Tekko) so that the pulp concentration was 28%. To the dry solid content of this dehydrated and concentrated pulp, 2% hydrogen peroxide, 2% sodium silicate, and 0.3% deinking agent (DI-600 R/manufactured by Kao) were added, followed by strong mechanical stirring ( Disperser/manufactured by Aikawa Iron Works) treatment was performed. This mechanically agitated pulp was heated at 50°C.
After leaving for 100 minutes (ripening), the pulp was taken out and diluted to a pulp concentration of 4%, followed by dispersion using a high-speed disintegrator (Top Finer, manufactured by Aikawa Tekko). [Foam flotation separation process] The above-mentioned dispersion pulp suspension was further diluted to a pulp concentration of 1.0%, and stirred while introducing air. TATER (manufactured by Aikawa Iron Works) was used for flotation separation treatment. [Post-treatment step] Subsequently, the pulp suspension that has undergone the flotation separation process is passed through a cleaner for removing heavy foreign matter and a device for removing light foreign matter (Giroclean/manufactured by Aikawa Iron Works) for treatment. After that, it was dehydrated and concentrated. [Results] The recycled pulp thus obtained was
Finished into handmade sheets according to APPI STD T218, and after air-drying, the whiteness was measured using an Ellejo brightness meter (Ellejo 200
0). A handmade sheet with a tension of 60 g/m2 was prepared and measured in accordance with JIS Sp8113. The whiteness and tension obtained at this time were 83, respectively.
%, 3.7 Kg. Separately, paper was made by blending this recycled pulp and virgin pulp (50:50), but no color developed when the paper was heated in a dryer (heating). In addition,
The results obtained are shown in Table 1. Example 2 [Disintegration process] Used heat-sensitive recording paper with a protective layer on a pulper (high-density pulper/manufactured by Aikawa Tekko), and 5% Na0H added to the used paper, and an antifoaming agent (Nopco) DF-122 (manufactured by San Nopco) was added at 0.03% based on the dry solid content, and the pulp density was 20.
% of warm water (30°C) and disintegrated for 40 minutes. [Screen process] The above pulp suspension was diluted to a pulp concentration of 3.5% and treated using a screen with a slit width of 0.2 mm (Fine Screen/manufactured by Aikawa Iron Works). did. [Mechanical stirring step] Next, the accept was dehydrated and concentrated using a dehydration concentrator (tilt extractor, screw press, manufactured by Aikawa Iron Works) so that the pulp concentration was 30%. To the dry solid content of this dehydrated and concentrated pulp, 5% hydrogen peroxide, 3% sodium silicate, and 0.3% deinking agent (DI-610/manufactured by Kao) were added, followed by mechanical stirring (disperser). / Aikawa Iron Works) treatment was performed. After this mechanically agitated pulp was left at 50°C for 100 minutes, the pulp was taken out and the pulp density was 4.
% and dispersed the pulp using a high-speed disintegrator (Top Finer, manufactured by Aikawa Iron Works). [Foam flotation separation process] The above-mentioned dispersion pulp suspension was further diluted to a pulp concentration of 1.0%, and stirred while introducing air. TATER/manufactured by Aikawa Iron Works) for flotation separation treatment. [Post-treatment step] Subsequently, the pulp suspension that has undergone the flotation separation process is passed through a cleaner for removing heavy foreign matter and a device for removing light foreign matter (Giroclean/manufactured by Aikawa Iron Works) for treatment. After that, it was dehydrated and concentrated. [Results] The thus obtained recycled pulp was treated in the same manner as in Example 1, and the whiteness and tension of the handsheet were measured and were 84% and 3.6 kg, respectively. The results obtained are shown in Table 1. Note that paper was made from the same pulp in the same manner as in Example 1, but no color developed in the paper dryer. Example 3 [Disintegration process] A waste paper of heat-sensitive recording paper having a protective layer on a pulper (high concentration pulper/manufactured by Aikawa Tekko), 1.5% NaOH was added to the waste paper, and an antifoaming agent was added to the waste paper. (Form Clean M-48/manufactured by Hakuto Kagaku Co., Ltd.) was added at 0.03% based on the dry solid content, and warm water (45°C) was added so that the pulp concentration was 25%.
Disaggregated for minutes. [Rough Screening Step] The above pulp suspension was diluted to a pulp concentration of 3.5%, and then mixed using a screen with a slit width of 0.3 mm (Fine Screen/manufactured by Aikawa Iron Works). Processed. [Mechanical stirring step] Next, the accept was dehydrated and concentrated using a dehydration concentrator (tilt extractor, screw press, manufactured by Aikawa Tekko) so that the pulp concentration was 30%. Hydrogen peroxide 0.5% and sodium silicate 1% based on the dry solid content of this dehydrated and concentrated pulp.
, 0.3% of a deinking agent (DI-610/manufactured by Kao) were added, and mechanical stirring (disperser/manufactured by Aikawa Iron Works) was performed. This mechanically agitated pulp is
After standing at 0℃ for 100 minutes, the pulp was taken out, diluted to a pulp concentration of 4%, and placed in a high-speed disintegrator (
The pulp was dispersed using Aikawa Iron Works (Top Finer). [Foam flotation separation process] The above dispersion pulp suspension was further diluted to a pulp concentration of 0.7%, stirred while introducing air, and processed into a foam flotation device (vertical flotator/ (manufactured by Aikawa Iron Works) to perform flotation separation treatment. [Screen process] The above pulp suspension was treated using a screen (Fine Screen/manufactured by Aikawa Iron Works) with a slit width of 0.2 mm. [Post-treatment step] Subsequently, the pulp suspension that has undergone the flotation separation process is passed through a cleaner for removing heavy foreign matter and a device for removing light foreign matter (Giroclean/manufactured by Aikawa Iron Works) for treatment. After that, it was dehydrated and concentrated. [Results] The thus obtained recycled pulp was treated in the same manner as in Example 1, and the whiteness and tension of the handsheet were measured, and were found to be 81% and 3.8 Kg, respectively. The results obtained are shown in Table 1. Note that paper was made from the same pulp in the same manner as in Example 1, but no color developed in the paper dryer. Example 4 [Disintegration process] Used heat-sensitive recording paper having a protective layer on the pulper (high-density pulper/manufactured by Aikawa Tekko), 2% NaOH added to the used paper, and an antifoaming agent (Nopco) 1407-K/manufactured by San Nopco Co., Ltd.) was added at 0.01% based on the dry solid content, and the pulp concentration was 15%.
Warm water (55°C) was added so that the mixture was disintegrated for 30 minutes. [Rough screening process] The above pulp suspension was diluted to a pulp concentration of 3.5%, and then mixed using a screen with a slit width of 0.25 mm (Fine Screen/manufactured by Aikawa Iron Works). Processed. [Mechanical stirring step] Next, the accept was dehydrated and concentrated using a dehydration concentrator (tilt extractor, screw press, manufactured by Aikawa Tekko) so that the pulp concentration was 25%. To the dry solid content of this dehydrated and concentrated pulp, 1% hydrogen peroxide, 1% sodium silicate, and 0.3% deinking agent (DI-610/manufactured by Kao) were added, followed by mechanical stirring (disperser). / Aikawa Iron Works) treatment was performed. After this mechanically agitated pulp was left at 50°C for 50 minutes, the pulp was taken out, diluted to a pulp concentration of 4%, and dispersed using a high-speed disintegrator (Top Finer, manufactured by Aikawa Iron Works). did. [Screening process] The pulp suspension obtained above was further diluted to a pulp concentration of 1.0%, and then passed through a screen (with a slit width of 0.2 mm).
Fine Screen/manufactured by Aikawa Tekko). [Foam flotation separation process] The above-mentioned dispersion pulp suspension is stirred while introducing air, and the foam flotation separation device (
A vertical flotator (manufactured by Aikawa Iron Works) was used for flotation separation. [Post-treatment process] Subsequently, the pulp suspension that has undergone the flotation separation process is passed through a cleaner for removing heavy foreign matter and a device for removing light foreign matter (Giroclean/manufactured by Aikawa Iron Works) for treatment. After that, it was dehydrated and concentrated. [Results] The thus obtained regenerated pulp was treated in the same manner as in Example 1, and the whiteness and tension of the handsheet were measured and found to be 81% and 3.7 Kg, respectively. The results obtained are shown in Table 1. Note that paper was made from the same pulp in the same manner as in Example 1, but no color developed in the paper dryer. Example 5 [Disintegration process] A waste paper of heat-sensitive recording paper having a protective layer on a pulper (high concentration pulper/manufactured by Aikawa Tekko), 1.25% NaOH was added to the waste paper, and an antifoaming agent was added to the waste paper. (Nopco 1407-K/manufactured by San Nopco Co., Ltd.) was added at 0.07% based on the dry solid content, warm water (58° C.) was added so that the pulp concentration was 15%, and disintegration was performed for 30 minutes. [Rough screening process] The above pulp suspension was diluted to a pulp concentration of 3.5%, and then mixed using a screen (double separator/manufactured by Aikawa Iron Works) with a slit width of 0.3 mm. Processed. [Mechanical stirring step] Next, the accept was dehydrated and concentrated using a dehydration concentrator (tilt extractor, screw press, manufactured by Aikawa Tekko) so that the pulp concentration was 33%. Based on the dry solid content of this dehydrated and concentrated pulp, 1% hydrogen peroxide, 2.5% sodium silicate,
0.6% of a deinking agent (DI-600R/manufactured by Kao) was added to each, and mechanical stirring (disperser/manufactured by Aikawa Iron Works) was performed. This mechanically agitated pulp is
After being left at 0°C for 120 minutes, the pulp was taken out, diluted to a pulp concentration of 4%, and placed in a high-speed disintegrator (
The pulp was dispersed using Top Finer (manufactured by Aikawa Tekko). [Foam flotation separation process] The above dispersion pulp suspension was further diluted to a pulp concentration of 1%, stirred while introducing air, and foam flotation device (vertical flotator/Aikawa Tekko Co., Ltd.) was used. The flotation separation process was carried out using the following methods: [Screen Step] The above pulp suspension was diluted to a concentration of 1% and subjected to a selective treatment using a screen with a slit width of 0.2 mm (Fine Screen/manufactured by Aikawa Tekko). [Post-treatment process] Subsequently, the pulp suspension that has undergone the flotation separation process is passed through a cleaner for removing heavy foreign matter and a device for removing light foreign matter (Giroclean/manufactured by Aikawa Iron Works) for treatment. After that, it was dehydrated and concentrated. [Results] The thus obtained recycled pulp was treated in the same manner as in Example 1, and the whiteness and tension of the handsheet were measured, and they were 82% and 3.8 Kg, respectively. The results obtained are shown in Table 1. Note that paper was made from the same pulp in the same manner as in Example 1, but no color developed in the paper dryer. Comparative Example 1 A recycled pulp was prepared and treated in the same manner as in Example 1, except that the addition of NaOH and antifoaming agent used in the disintegration step was stopped. The tension of the handmade sheet of recycled pulp obtained at this time was 3.8 kg, but the El Rejo whiteness was 60%, which was quite poor compared to Example 1. )
The paper made with this mixture developed a little color in the dryer. The results obtained are shown in Table 1. Comparative Example 2 The preparation and treatment were carried out in the same manner as in Example 1, except that the addition of the antifoaming agent used in the defibration step was stopped and the temperature of the hot water was changed to 70°C. Obtained pulp. The tension of the handmade sheet of recycled pulp obtained at this time was 3
．． 7 kg, but the El Rejo whiteness was 70%, which was poor compared to Example 1.
The paper made with a blend of 0:50) developed a little color in the dryer. The results obtained are shown in Table 1. Comparative Example 3 The preparation and treatment were carried out in the same manner as in Example 1 except that the addition of the antifoaming agent used in the defibration step was stopped and the pulp concentration was changed to 6%. Obtained pulp. The tension of the handmade sheet of recycled pulp obtained at this time was 3.9 kg, but the El Rejo whiteness was 73%, which was poor compared to Example 1. The paper made with the blend developed a little color in the dryer. The results obtained are shown in Table 1. Comparative Example 4 The preparation and treatment were carried out in the same manner as in Example 1 except that the addition of NaOH was changed to 1.2%.
Regenerated pulp was obtained. The Elleho whiteness of the recycled pulp obtained at this time was 83%, which is the same as in Example 1, but the tension of the handsheet was reduced to 3.0 kg. The results obtained are shown in Table 1. Comparative Example 5 In Example 1, the amount of NaOH used in the disintegration step was 0.5%, and the pulp concentration in the mechanical stirring step was 10%.
Regenerated pulp was obtained by preparing and treating in the same manner as in Example 1, except that the respective percentages were changed. The tension of the handmade sheet of recycled pulp obtained at this time was 3.7 kg, but the El Rejo whiteness was 62%, which was considerably worse than that of Example 1, and the recycled pulp and virgin pulp (50:5
Paper made with 0) produced granular colored spots when exposed to a dryer. The results obtained are shown in Table 1. [Table 1] [Effects of the Invention] As is clear from the examples, recycled pulp obtained from waste heat-sensitive recording paper provided with a protective layer can maintain high whiteness; Moreover, even when the paper sheet obtained from the recycled pulp of the waste paper was heated, no color development or granular colored spots were observed.

Claims

[Claims] Claim 1: A method in which waste heat-sensitive recording paper is disintegrated into a disintegrated pulp in an aqueous NaOH solution, a deinking agent and a peroxide are added, and then the disintegrated pulp is subjected to high-concentration mechanical stirring treatment, A method for producing recycled pulp from waste heat-sensitive recording paper, which is characterized in that it is processed so as to satisfy the following conditions (a) to (d). (a); The NaOH aqueous solution contains an antifoaming agent (b);
The concentration of NaOH is 1 to 10% by weight based on the waste paper pulp (c); The temperature of the NaOH aqueous solution during disintegration is 30 to 6% by weight
0℃(d); The concentration of waste paper pulp at the time of disintegration is 10% by weight or more 2. The recycled pulping method according to claim 1, wherein the thermosensitive recording paper has a protective layer.